A Model of Temporal Intensity Modulation for Laser Generated Ultrasound

Sanderson, Terry; Ume, Charles; Jarzynski, Jacek

doi:10.1007/978-1-4615-5947-4_79

Cited by 2 publications

(3 citation statements)

References 11 publications

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“…8. This numerical model is similar to models developed previously by Schliechert et aL (9) and Spicer,(1~ both of whom obtained excellent agreement between their numerical results and experiment.…”

Section: Analytical Modelsupporting

confidence: 75%

A comparison of Q-switched and intensity modulated laser pulses for ultrasonic NDT

1998

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The purpose of this work was to investigate the potential of intensity modulated laser pulses for ultrasonic signal enhancement in NDT using a numerical model. Q-switched lasers produce broadband ultrasound which is susceptible to measurement noise. Intensity modulation can alleviate this problem by focussing the ultrasonic energy into a band centered around the modulation frequency. Ultrasonic waveforms and their DFTs are considered here in both aluminum and steel for a wide range of observation angles, for Q-switched laser pulses and for a 1 MHz intensity modulated laser pulse. These waveforms are useful to NDT researchers because they indicate what kinds of signals can be expected from unflawed materials. It is found that P waves are not as easily enhanced by modulation as are SV or Rayleigh surface waves. The time window which should be used to measure ultrasonic signals produced by intensity modulated laser pulses is determined.

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Section: Analytical Modelsupporting

confidence: 75%

A comparison of Q-switched and intensity modulated laser pulses for ultrasonic NDT

1998

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“…This transient increase in local temperature induces thermal expansion and generates an elastic wave under the thermoelastic effect. Within this thermoelastic regime, we can consider the source as a central expansion source consisting of three equal orthog-onal force dipoles given by [11,12]…”

Section: -10mentioning

confidence: 99%

“…Nevertheless, quantitative analysis of the precursor could not be achieved using the body force source model alone. Furthermore, Sanderson et al [11,12] proposed a model comprising a thermal dipole and a surface center of expansion, validated through finite element (FE) simulations and experimental findings. This model is the prevailing source model utilized in the context of the thermoelastic effect.…”

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of laser-generated ultrasonic wave characteristics and their correlation with grain size in polycrystalline materials

Xu 徐,

Bai 白,

Ma 马

et al. 2024

Chinese Phys. B

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The quantitative relationship between nanosecond pulsed laser parameters and the characteristics of laser-generated ultrasonic waves in polycrystalline materials was evaluated. The high energy of the pulsed laser with a large irradiation spot simultaneously generated ultrasonic longitudinal and shear waves at the epicenter under the slight ablation regime. An optimized denoising technique based on wavelet thresholding and variational mode decomposition was applied to reduce noise in shear waves with a low signal-to-noise ratio. An approach for characterizing grain size was proposed using spectral center frequency ratio (SCFR) based on time-frequency analysis. The results have demonstrated that the generation regime of ultrasonic waves is not solely determined by the laser power density; even at high power densities, a high energy with a large spot can generate an ultrasonic waveform dominated by the thermoelastic effect. It is ascribed to the intensification of the thermoelastic effect with the proportional increase in laser irradiation spot area for a given laser power density. Furthermore, both longitudinal and shear wave SCFRs are linearly related to grain size in polycrystalline materials; however, the shear wave SCFR is more sensitive to finer-grained materials. This study holds great significance for evaluating metal material properties using laser ultrasound.

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A Model of Temporal Intensity Modulation for Laser Generated Ultrasound

Cited by 2 publications

References 11 publications

A comparison of Q-switched and intensity modulated laser pulses for ultrasonic NDT

A comparison of Q-switched and intensity modulated laser pulses for ultrasonic NDT

Quantitative analysis of laser-generated ultrasonic wave characteristics and their correlation with grain size in polycrystalline materials

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